G'day choroba,

++ Many thanks for this.

The namespace extension ($ns_extension) can contain several parts, e.g. A::B::C, so I made a slight adjustment to handle that. I also pared the code, bit by bit, to end up with the simplified:

sub dynamic_require {
    my ($self, $ns_extension) = @_;

    my $class = join '::', __PACKAGE__, $ns_extension;
    my $source = <<~EOF;
        package $class;
        use parent 'MooselessRequireHookTest';
        1;
        EOF
    push @INC, sub {
        my ($coderef, $filename) = @_;
        my $wanted_filename = $class =~ s{::}{/}gr . '.pm';
        return unless $filename eq $wanted_filename;
        return \$source;
    };
    eval "require $class;";

    return;
}
[download]

I added a couple more tests:

$rht->dynamic_require('A::B::C');
my $rht_abc = MooselessRequireHookTest::A::B::C->new();
is(defined $rht_abc, 1, 'Test MooselessRequireHookTest::A::B::C->new()
+');
isa_ok($rht_abc, 'MooselessRequireHookTest::A::B::C', 'Test MooselessR
+equireHookTest::A::B::C->new() ISA');
[download]

I also added this temporary debug line after unpacking @_:

warn "\$coderef[$coderef] \$filename[$filename]\n";
[download]

Now, all tests are successful and I have a little more insight into what is going on:

sscce_mooseless_require_hook_test.t ..
1..8
ok 1 - Test MooselessRequireHookTest::->new()
ok 2 - 'Test MooselessRequireHookTest::->new() ISA' isa 'MooselessRequ
+ireHookTest'
ok 3 - Test MooselessRequireHookTest::Test1->new()
ok 4 - 'Test MooselessRequireHookTest::Test1->new() ISA' isa 'Mooseles
+sRequireHookTest::Test1'
ok 5 - Test MooselessRequireHookTest::Test2->new()
ok 6 - 'Test MooselessRequireHookTest::Test2->new() ISA' isa 'Mooseles
+sRequireHookTest::Test2'
ok 7 - Test MooselessRequireHookTest::A::B::C->new()
ok 8 - 'Test MooselessRequireHookTest::A::B::C->new() ISA' isa 'Moosel
+essRequireHookTest::A::B::C'
$coderef[CODE(0x60008aa00)] $filename[MooselessRequireHookTest/Test1.p
+m]
$coderef[CODE(0x60008aa00)] $filename[MooselessRequireHookTest/Test2.p
+m]
$coderef[CODE(0x600868c78)] $filename[MooselessRequireHookTest/Test2.p
+m]
$coderef[CODE(0x60008aa00)] $filename[MooselessRequireHookTest/A/B/C.p
+m]
$coderef[CODE(0x600868c78)] $filename[MooselessRequireHookTest/A/B/C.p
+m]
$coderef[CODE(0x60086da88)] $filename[MooselessRequireHookTest/A/B/C.p
+m]
ok
All tests successful.
Files=1, Tests=8,  0 wallclock secs ( 0.00 usr  0.03 sys +  0.08 cusr 
+ 0.03 csys =  0.14 CPU)
Result: PASS
[download]

The mechanism behind this is a mystery to me. Why is it calling the subroutine with all the previous CODEREF values then the newly created CODEREF? Anyway, what you provided weeds out all of the unwanted parts. @INC ends up with: the use lib dir; the 4 usual dirs; and 3 (hook) CODEREFs.

/home/ken/tmp/pm_sscce_require_hook/lib
/home/ken/perl5/perlbrew/perls/perl-5.32.0/lib/site_perl/5.32.0/cygwin
+-thread-multi
/home/ken/perl5/perlbrew/perls/perl-5.32.0/lib/site_perl/5.32.0
/home/ken/perl5/perlbrew/perls/perl-5.32.0/lib/5.32.0/cygwin-thread-mu
+lti
/home/ken/perl5/perlbrew/perls/perl-5.32.0/lib/5.32.0
CODE(0x60008aa00)
CODE(0x600868c78)
CODE(0x60086da88)
[download]

As I suspected, the issue had nothing to do with Moose. I applied these changes to my original module and all of its tests now pass. Thanks again.